This invention relates generally to gas turbine engines and, more particularly, to a rotor and shroud apparatus and method of assembly.
In the normal practice of assembling stationary shrouds and related hardware around a turbine rotor, there occurs an inherent eccentricity between the running center of the rotating member and the surrounding stationary structural components. The primary reason for this eccentricity is the unavoidable stack-up of the machining tolerances in the combination of the various structural members between the bearings and the turbine shroud. This tolerance stack-up in a typical gas turbine engine can be on the order of 0.005 to 0.015 inch and, considering that this eccentricity must be accommodated by increased clearances, it may represent an approximate one-half to one and one-half points of loss in turbine efficiency.
One method by which the eccentricities may be reduced so as to not require the increased clearances is by way of machining after assembly. In the case of a turbomachine where the high pressure turbine is the primary focus of concentricity, this requires the mounting of the entire low pressure turbine rotor and structural components on a vertical turret lathe and machining the high pressure turbine shrouds as accurately as possible so as to be concentric with the bearing. Not only is this process difficult and time consuming, but it also requires the use of expensive tooling and facilities.
Another disadvantage of the machining process is that concentricity or near-concentricity is achieved only for that particular combination of hardware. If in the normal deterioration of the engine, the structural components tend to wear and distort, eccentricities will tend to re-appear and increase with age, thus requiring another time-consuming and expensive machining process for correction. Further, in the refurbishment of the engine, if certain components are replaced or interchanged, the resulting eccentricity must again be accounted for in this undesirable manner.
It is therefore an object of the present invention to provide a rotor and shroud combination which is substantially in concentric relationship.
Another object of the present invention is the provision in a turbomachine for the reduction in eccentricity between the rotor bearings and the stationary shroud surrounding the rotor.
Yet another object of the present invention is the provision in a turbomachine for the elimination of expensive machining processes in order to obtain relative concentricity between the rotor bearing and the rotor shroud.
Still another object of the present invention is the provision in a turbofan engine for increased efficiency.
Another object of the present invention is the provision for the economic assembly of rotating turbine and stationary shroud components.
A further object of the present invention is the provision of an economical and effective method and apparatus for obtaining substantial concentricity between a rotor and a surrounding stationary shroud.
These objects and other features and advantages become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.